Questions And Answers

We are installing new SMT machines and the people without ESD protective equipment needs to walk near of the ESDS devices. IPC-VT-19 says that electrostatic discharge can occur even 3 feet distance to ESDS devices. Is this true? - Anonymous, Mexico City, Mexico

Answer

A 3 foot discharge would be rather amazing for a person. (If someone had a 3 foot discharge emanate from their body they would have to be at 100’s of kilovolts….maybe megavolts [think it’s 10kV/inch in air]…..and don’t forget to dial 911…forget the damaged board). A typical older industry standard ask that you keep 1 foot away from ESDS devices. But now that devices are sensitive to lower voltages, maybe a few more inches wouldn’t hurt. The big problem may be charge induction from un-grounded people walking nearby an ESDS device. No discharge occurs, but if they are charged up enough to have a large enough electric field it is possible to induce charges (even though not very large [millivolts to volts]) on non-grounded conductors on an ESDS device. For this to happen, you would have to have a rather significant charge on your body to begin with [10’s of kilovolts].